Ask HN: Why is my streaming video so slow

I spend most of my TV time in the evenings streaming shows or movies, and while some work well, other services show lots of problems. I can't believe that there isn't a good tool to find out where the connection is breaking down, but after searching I have been unable to find one. How do I find the bottleneck?

If the problem is with my WiFi router (cheap 802.11n model) I am happy to put in money for an upgrade. If the problem is with my internet service (15Mbps) I am happy to pay a little more. I just don't want to throw money away since I can't believe that either of these should really be the issue. Is there a good tool for diagnosing the problem that I just haven't found yet?